The present invention relates to grinding wheel abrading tools, and more particularly, to large-diameter, large-width grinding wheels having a peripheral workface formed by a plurality of geometrically-shaped superabrasive plates.
Large-diameter, typically greater than ten inch, and large-width, typically greater than one and one-half inch, superabrasive grinding wheel abrading tools are commonly manufactured as either continuous-rim or segmental wheels. The superabrasive material used for the manufacture of both continuous-rim or segmental wheels is generally diamond or cubic boron nitride.
Conventional abrasives, such as aluminum oxide and silicon carbide, used as the primary abrasive in conventional grinding wheels, are also used as a secondary abrasive or filler in superabrasive grinding wheels. Conventional abrasives additionally are used for the manufacture of backing layers and as a core material for the manufacture of wheel centers in superabrasive grinding wheels.
Both continuous-rim and segmental wheels are manufactured by combining the desired abrasive materials with an organic resin binder, traditionally thermoset plastics such as phenolics and polyamides, metallic binders, traditionally comprising copper, brass, tin, silver and cast iron, and ceramic binders, typically comprising glass, clays and feldspars. The combination comprising the abrasive and the binder are formed to the desired geometry by hot pressing or cold pressing.
In hot pressing, the materials are placed in a suitable mold and simultaneously placed under pressures, typically ranging from one-thousand to ten-thousand pounds per square inch and temperatures, typically ranging from three-hundred to eighteen-hundred degrees Fahrenheit. Hot pressing is generally used to manufacture most resin and metal bonded grinding wheels as the processing temperatures are low to mid range. The molds used for resin bonding are typically aluminum or steel. The molds used for metal bonding are typically steel or graphite.
In cold pressing, the materials are placed in a suitable mold and placed under pressures, typically ranging from one-thousand to five-thousand pounds per square inch, at room temperature. The compacted material is removed from the mold and separately sintered at temperatures typically ranging from thirteen-hundred to twenty-three hundred degrees Farenheit. Cold pressing is generally used to manufacture vitrified (ceramic bonded) grinding wheels as the processing temperatures are typically destructive to common mold materials.
For the above reasons, grinding wheel manufacturers must invest in large tooling and equipment such as powerful hydraulic presses, high-temperature kilns and finishing equipment. Practical limitations regarding the equipment and the inherent problems in maintaining material consistency and dimensionality when manufacturing large molded wheels have consequently led manufacturers to fabricate composite large-diameter, large-width wheels from two or more wheels whose widths taken together equal the desired width.
The presence of seams in large-diameter, large-width superabrasive continuous-rim grinding wheel abrading tools assembled from multiple continuous-rim wheels of lesser width adversely effects the quality of the surface of a workpiece. The continuous circumferential seams between the component wheels produce grinding marks and spiral marks in the respective workpieces for plunge grinding, centerless grinding and through-feed centerless grinding applications. Attempts have been made to eliminate such grinding imperfections by having a bias angle between the component wheels, thereby creating seams that vary in location as the wheel rotates. However, the angle-biased components have not eliminated grinding imperfections. The position varying seams create areas of poor finish on the workpiece surfaces.
Segmental grinding wheels have abrading plates of superabrasive material epoxy-bonded to the circumferential surface of a wheel center or core. Traditional narrow-width segmental grinding wheel concepts typically have a single row of rectangular or parallelogram-shaped abrading plates epoxy-bonded to the circumferential surface of the wheel core. As wheel widths have increased, additional rows of abrading plates have been added to achieve a superabrasive circumferential surface of the desired width.
The presence of continuous circumferential seams between the rows of abrading plates produce grinding marks and spiral marks in the various workpieces. Attempts have been made to eliminate such grinding imperfections by staggering the alignment of the abrading plates to disrupt the continuous circumferential seams. Although staggering the alignment of the abrading plates reduces workpiece grind marks, they are not eliminated. Furthermore, the seams that are aligned parallel to the axis of wheel rotation cause harmonic vibrations in the grinding system as they are momentarily in straight-line contact with the workpiece.
A large-diameter, large-width segmental superabrasive grinding wheel abrading tool that overcomes the aforementioned limitations by having staggered abrading plates with angular sides is highly desirable as staggering the angular sided abrading plates eliminates continuous circumferential seams and line contact between the workpiece and the grinding wheel, thereby allowing a machinist to precision grind workpieces having minimal grinding imperfections.
One aspect of the present invention relates to an abrading tool comprising a rotatable body of revolution having an axis of rotation and a peripheral workface fixedly attached to a curved surface of the body of revolution. The workface is formed by a plurality of discrete, geometrically-shaped abrading plates disposed in a generally contiguous relationship. Lines-of-juncture are formed by opposed edges of adjacent abrading plates. Any diametrical plane, having at least one coplanar line-of-juncture, has a discontinuous coplanar curve, at least a portion thereof being the at least one coplanar line-of juncture. Additionally, any longitudinal plane, having at least two coplanar lines-of-juncture, has opposed ends of the at least two coplanar lines-of-juncture being spaced apart.
Another aspect of the invention relates to an abrading tool comprising a rotatable body of revolution having an axis of rotation and a peripheral workface fixedly attached to a curved surface of the body of revolution. The workface is formed by a plurality of discrete, geometrically-shaped abrading plates disposed in a generally contiguous relationship. Lines-of-juncture are formed by opposed edges of adjacent abrading plates. All lines-of-juncture are oriented at an angle to the axis of rotation. Any diametrical plane, having at least one coplanar line-of-juncture, has a discontinuous coplanar curve, at least a portion thereof being the at least one coplanar line-of juncture.
Another aspect of the invention relates to an abrading tool comprising a rotatable body of revolution having an axis of rotation and a peripheral workface fixedly attached to a curved surface of the body of revolution. The workface is formed by a plurality of discrete, geometrically-shaped abrading plates disposed in a generally contiguous relationship. Lines-of-juncture are formed by opposed edges of adjacent abrading plates. All lines-of-juncture are oriented at a non-perpendicular angle to the axis of rotation.
Another aspect of the invention relates to an abrading plate for being attached to a curved surface of a rotatable body of revolution for the grinding of a workpiece comprising a hexagonal-shaped plate including a first mounting surface having a curvature which corresponds to the curvature of a portion of the curved surface of a rotatable body of revolution. The hexagonal-shaped plate has opposed first and fourth vertices lying in a diametrical plane of the rotatable body of revolution and radially extending side surfaces with a variable angle bevel adjacent to the first and fourth vertices. Upon orientation of the hexagonal-shaped plate such that the opposed first and fourth vertices lie in a diametrical plane of the rotatable body of revolution and upon the fixed attachment of the hexagonal-shaped plate to the curved surface of the rotatable body of revolution, a portion of a peripheral workface of an abrading tool is formed.
Still another aspect of the invention relates to an abrading plate for being attached to a curved surface of a rotatable body of revolution for the grinding of a workpiece comprising a parallelogram-shaped plate including a first mounting surface having a curvature which corresponds to the curvature of a portion of the curved surface of a rotatable body of revolution. The parallelogram-shaped plate has parallel first and third radially extending side surfaces with a variable bevel angle. Upon orientation of the parallelogram-shaped plate such that the first and third radially extending side surfaces intersect at an angle with a diametrical plane of the rotatable body of revolution and upon the fixed attachment of the parallelogram-shaped plate to the curved surface of the rotatable body of revolution, a portion of a peripheral workface of an abrading tool is formed.